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// Copyright (c) The Diem Core Contributors
// SPDX-License-Identifier: Apache-2.0

// Copyright 2021 Conflux Foundation. All rights reserved.
// Conflux is free software and distributed under GNU General Public License.
// See http://www.gnu.org/licenses/

//! This module defines physical storage schema for an event index via which a
//! ContractEvent ( represented by a <txn_version, event_idx> tuple so that it
//! can be fetched from `EventSchema`) can be found by <access_path, version,
//! sequence_num> tuple.
//!
//! ```text
//! |<--------------key------------>|<-value->|
//! | event_key | txn_ver | seq_num |   idx   |
//! ```

use crate::schema::{ensure_slice_len_eq, EVENT_BY_VERSION_CF_NAME};
use anyhow::Result;
use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
use diem_types::{event::EventKey, transaction::Version};
use schemadb::{
    define_schema,
    schema::{KeyCodec, ValueCodec},
};
use std::{convert::TryFrom, mem::size_of};

define_schema!(EventByVersionSchema, Key, Value, EVENT_BY_VERSION_CF_NAME);

type Key = (EventKey, Version);

type Index = u64;
type Value = Index;

impl KeyCodec<EventByVersionSchema> for Key {
    fn encode_key(&self) -> Result<Vec<u8>> {
        let (ref event_key, version) = *self;

        let mut encoded = event_key.to_vec();
        encoded.write_u64::<BigEndian>(version)?;

        Ok(encoded)
    }

    fn decode_key(data: &[u8]) -> Result<Self> {
        ensure_slice_len_eq(data, size_of::<Self>())?;

        const EVENT_KEY_LEN: usize = size_of::<EventKey>();
        let event_key = EventKey::try_from(&data[..EVENT_KEY_LEN])?;
        let version = (&data[EVENT_KEY_LEN..]).read_u64::<BigEndian>()?;

        Ok((event_key, version))
    }
}

impl ValueCodec<EventByVersionSchema> for Value {
    fn encode_value(&self) -> Result<Vec<u8>> {
        Ok(self.to_be_bytes().to_vec())
    }

    fn decode_value(mut data: &[u8]) -> Result<Self> {
        ensure_slice_len_eq(data, size_of::<Self>())?;

        Ok(data.read_u64::<BigEndian>()?)
    }
}

#[cfg(test)]
mod test;